The present invention relates to x-ray generating apparatus, and in particular to x-ray tubes with an improved unitary vacuum housing design which allows for a radiation protection and direct heat transmission through a body of the unitary vacuum housing.
The x-ray generating apparatus generally comprises a vacuum enclosure with an anode assembly and a cathode assembly spaced therebetween. The cathode assembly comprises an electron emitting cathode which is disposed so as to direct a beam of electrons onto a focal spot of an anode target of the anode assembly. In operation, electrons emitting by the cathode are accelerated towards the anode target by a high voltage created between the cathode and the anode target. The accelerated electrons impinge on the focal spot area of the anode target with sufficient kinetic energy to generate a beam of x-rays which passes through a window in the vacuum enclosure.
However, only about one percent of the input energy is converted into x-radiation. The vast majority of the input energy is converted into thermal energy which is stored in the mass of the anode assembly. It is known in the art that by rotating the anode the heat generated during x-ray production can be spread over a larger anode target area. To improve the heat transfer by radiation the anode assembly is coated in a special way and is cooled by forced convection with, for example, a dielectric liquid as disclosed in the U.S. Pat. No. 4,928,296. The excessive thermal energy from the anode assembly is dissipated by thermal radiation to the surrounding enclosure.
In conventionally designed x-ray generating apparatus the vacuum enclosure is placed in a housing which serves as a container for cooling medium, typically cooling fluid or the forced air. In fluid cooled x-ray apparatus, the type disclosed for example in the U.S. Pat. No. 4,841,557, the rotating anode x-ray tube is immersed into the housing filled with an insulating fluid such as a transformer oil which is circulated by a pump for at least partially dissipating the heat from the vacuum enclosure.
The air cooled x-ray tube disclosed in the U.S. Pat. No. 5,056,126 comprises a housing with disposed therein an evacuated envelope having a cathode and an anode that are capable of being biased to a voltage in a range between about 1 kV and 200 kV, and a heat cage formed of a heat conducting material. The heat cage is provided within the interior of the vacuum enclosure surrounding an anode target. The heat cage absorbs heat from the anode and transports it to the end portion of the vacuum enclosure, and then to the exterior of the housing for dissipation by the air flow. The excessive radiation from the x-ray tube is blocked from exiting the housing by a lead liner which is provided between the evacuated envelope and the housing. The lead liner serves also as a massive heat sink for the x-ray tube.
Being advantageous in some respects the air cooled tube design has certain drawbacks. The presence of the heat cage inside the evacuated envelope elongates the heat path leading to a heat dissipation which results in excessive temperature built up over the exterior of the vacuum enclosure which may damage the lead liner.
Therefore it is an object of the present invention to provide a compact x-ray generating apparatus with reduced number of components resulting increased reliability and reduced manufacturing costs.
It is another object of the present invention to provide the x-ray generating apparatus having a multi-functional vacuum enclosure which serves as a radiation shield, as a heat reservoir for balancing the temperature within the vacuum enclosure in case of power loss and as a direct heat transfer element between an anode assembly and an air cooling system.
It is yet another object of the present invention to provide the air cooling, x-ray generating apparatus comprising a multi-functional mounting block which serves as an installation element, as a heat reservoir and as an element of a cooling system.